The present invention relates to a method of forming a semiconductor device, and more particularly to a method of burying contact holes with a metal for forming multilevel interconnections.
In recent years, requirements for a high density integration of a semiconductor device and multilevel interconnections have been on the increase whereby it is also required to reduce the width of internal interconnections. The reduction in width of the interconnections requires forming a contact hole of a high aspect ratio. In prior art, however, it was difficult to exactly bury the contact hole of a high aspect ratio with a metal without forming any void.
In order to settle the above problem, it was proposed to bury the contact hole with the metal as follows. First, a refractory metal film is formed over an insulation film with a contact hole already formed on a substrate for subsequent formations of a titanium nitride film and an aluminum alloy film over them before the substrate is heated up to a temperature of 300.degree. C. for receipt of irradiation of a laser beam to thereby cause a reflow of the aluminum alloy so that the contact hole is buried with the aluminum alloy. It is also possible to prevent the aluminum alloy. This technique is disclosed in the Japanese laid-open patent publication No. 3-131029.
As described above, the substrate is heated up to a temperature of 300.degree. C. for a laser beam irradiation thereonto. In this case, a barrier metal layer of titanium nitride is heated to a temperature of about 600.degree. C. which is above a critical temperature of 500.degree. C. over which a chemical reaction of aluminum alloy with nitrogen in titanium nitride for the barrier metal. As a result, an aluminum nitride film is formed, which is highly resistive, for which reason a highly resistive contact is formed.
There was proposed another technique which is disclosed in the Japanese laid-open patent publication No. 2-271634. In this technique, a substrate is heated up to a temperature of not less than 450.degree. C. and below a melting point of aluminum or aluminum alloy so as to carry out a vacuum evaporation of aluminum or aluminum alloy onto a surface of the substrate whereby the contact hole is buried with the aluminum or aluminum alloy.
As described above, the substrate is heated up to a temperature of not less than 450.degree. C. for vacuum evaporation. However, the growth rate is slow and it is difficult to obtain a uniformity in level of substrate surface. Further, there is a possibility of a diffusion of an interconnection material into a semiconductor region. It is furthermore difficult to obtain a strong adhesion between the semiconductor region and the insulation film.
There was proposed still another technique which is disclosed in the Japanese laid-open patent publication No. 62-123714. In this technique, a substrate with a rough surface has been placed in an atmosphere including a steam of an organic metal before the substrate is cooled down so as to cause the organic metal to be adhered onto the rough surface of the substrate. A light is irradiated onto a predetermined portion of the organic metal film covering the rough surface of the substrate so as to cause a decomposition of the organic metal for formation of a metal interconnection layer.
As described above, the light energy is used for causing the decomposition of the organic metal, for which reason a reflective light from an interior of the contact hole results in locally insufficient or locally excessive decomposition of the organic metal. It is, therefore, difficult to bury the contact hole of a high aspect ratio, for example, 3-4 with a metal uniformly.
In the above circumstances, it had been required to develop a novel method of burying a contact hole having a high aspect ratio of about 4 with aluminum or aluminum alloy without formation of any void.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio with aluminum or aluminum alloy without formation of any highly resistive film such as titanium nitride film.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio with aluminum or aluminum alloy to ensure a high conductivity of a semiconductor region of a semiconductor substrate.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio with aluminum or aluminum alloy without heating the semiconductor region of the substrate up to a temperature of over 450.degree. C.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio with aluminum or aluminum alloy without causing any diffusion of an interconnection material into a semiconductor region of the substrate.
It had also been required to develop a novel method of burying a large number of contact holes, each of which has a high aspect ratio, with aluminum or aluminum alloy uniformly.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio to allow planarization of a surface of a lower level interconnection for realization of multilevel interconnections.
It had also been required to develop a novel method of burying a contact hole having a high aspect ratio to improve a reliability of electrode/interconnection processes for a device designed in accordance with the 0.25 .mu.m design rule to obtain a highly reliable semiconductor device.